Resize Image to KB

JPG and WebP files have a quality setting, and file size goes down as quality goes down. The tool runs a binary search on that setting: it tries the highest quality, checks the bytes, then halves the range again and again until it finds the highest quality whose file is still under your target. That takes about eight test encodes.

If the image would need heavy compression at its original pixel size, it is scaled down instead. A small test encode estimates how many pixels fit at a good quality, the search runs at that size (never below 50% quality), and the size is nudged up while the result still fits at high quality. Only very small images may go below 50%; you see the final quality next to each file.

With exact pixel dimensions on, the size never changes. Only the quality moves, and if the target cannot be met even at the lowest quality, the tool tells you instead of producing a wrong size.

"50 KB" can mean 50,000 bytes or 51,200 bytes (50 x 1,024, strictly called KiB). Windows shows sizes using 1,024, macOS uses 1,000, and websites are split. In Safe mode the file is kept at or under 1,000 bytes per KB, so it passes either check. Choose 1 KB = 1,024 B only if you know the site counts that way and you want the extra few percent of quality.

A minimum size is counted the other way, at 1,024 bytes per KB, for the same reason. If a picture is naturally smaller than your minimum, the tool raises the quality and can pad the JPG with an empty comment block; viewers ignore it, so the picture is unchanged.

Faces and text are where heavy compression shows first. If a form allows a range, aim near the top of it. For documents with small print, give the file at least 100 to 200 KB, or crop to the part that matters.